1. Field of the Invention
The present invention relates to a toner for use in an electrophotographic method, an electrostatic recording method, a magnetic recording method and a toner-jet method.
2. Description of the Related Art
Conventionally, in the electrophotographic method, an electrostatic charge image is formed on a photosensitive member by various means and subsequently the electrostatic charge image is developed by use of a toner to form a toner image on the photosensitive member. The toner image is, if necessary, transferred onto a transfer material such as paper. Thereafter, the toner image is fixed on the transfer material by applying, e.g., heat, pressure, heat/pressure or a vaporized solvent to obtain an image.
As a process for fixing a toner image, for example, a heat pressurizing method by a heat roller (hereinafter referred to as a heat roller fixing method) and a heat fixing method for fixing an image while bringing a sheet onto which the image is to be fixed into contact with a heating body with a fixing film interposed between them (hereinafter referred to as a film fixing method) have been developed.
In the heat roller fixing method and the film fixing method, a toner image on the sheet onto which the toner image is to be fixed is moved on the surface of the heat roller or the fixing film while keeping the toner image in contact therewith under pressure by a pressurizing member provided in contact therewith. In the fixing method, since the surface of the heat roller or the fixing film is in contact with the toner image of the sheet onto which the toner image is to be fixed under pressure, the thermal efficiency for fixing the toner image onto the sheet by fusion is extremely high, with the result that fixation can be quickly and satisfactorily performed. Particularly, the film fixing method has a large effect upon energy-saving. In addition, another effect is expected. For example, time required from the power-on time of an electrophotographic apparatus until the first print is completed can be reduced.
Various requests have been made for the electrophotographic apparatus, including the formation of a high-quality image, reduction in size/weight, high-speed operation with a high productivity and energy saving. Of them, particularly in a fixing process, it has been important, as technical problems, to achieve a further high-speed operation, reduce more energy and develop a system and material capable of attaining a highly reliable operation. However, to solve these problems by the heat roller fixing method and the film fixing method, it is essential to improve particularly the fixing performance of toner to a large extent. More specifically, the fixing performance for fixing a toner image to a sheet (onto which the toner image is to be fixed) sufficiently at a further lower temperature (hereinafter referred to as low-temperature fixing performance) must be improved. However, when an improvement of the low-temperature fixing performance is attempted, the performance of suppressing aggregation and fusion phenomena of toner during a long storage time (hereinafter referred to as anti-blocking performance) and the performance of suppressing formation of defective images when a large number of prints are continuously made (hereinafter referred to as running stability performance) tend to decrease. Therefore, it has been desired to develop a toner satisfying all of these performances. Furthermore, it is also necessary to improve a performance of preventing offset, which is a phenomenon where a next transfer material is stained with a toner undesirably deposited onto a fixing member such as a roller or a film (hereinafter referred to as anti-offset performance). Moreover, with the spread of full-color electrophotographic apparatuses, a new request for improving image quality has been made. To be more specific, a performance of improving a color development by forming a highly glossy image (hereinafter referred to as glossing performance) and a performance of suppressing unevenness of gloss in an image (hereinafter referred to anti-soaking performance) are required. The anti-soaking performance tends to emerge as deterioration of image quality. This is caused when the first half (in the moving direction thereof) of a transfer material such as paper is heated unevenly from the second half or when the first paper sheet is heated unevenly from the tenth paper sheet by increasing a discharge speed.
As the toner used for heat and pressure fixation and attempted to have well-balanced, low-temperature fixing performance and anti-blocking performance, a toner having a capsule structure is known (see Japanese Patent Application Laid-Open Nos. H06-130713 and H09-043896). These toners have an inner nuclear layer having a low glass transition point (Tg) covered with an outer shell layer having a high Tg. In this way, the low-Tg material contained in the interior of a toner particle is prevented from bleeding out, thereby providing low-temperature fixing performance and anti-blocking performance or running stability performance in a balanced manner. Furthermore, a toner having a cover layer of resin microparticles has good fixing performance, anti-blocking performance and running stability performance (see Japanese Patent Application Laid-Open Nos. 2003-091093 and 2004-226572). In another approach for improving the low-temperature fixing performance of a toner, there is provide a toner which has a controlled change of thermal physical property before and after the fusion of toner (see Japanese Patent Application Laid-Open No. 2006-084743). According to this toner, the low-temperature fixing performance and anti-blocking performance can be simultaneously achieved. However, it is difficult for these toners to satisfy all performances mentioned above when the low-temperature fixing performance is further improved.